1. Field of the Invention
This invention relates generally to an industrial process, and, more particularly, to adjusting a sampling rate of processed workpieces based on state estimation results.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the quality, reliability and throughput of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for higher quality computers and electronic devices that operate more reliably. These demands have resulted in a continual improvement in the manufacture of semiconductor devices, e.g., transistors, as well as in the manufacture of integrated circuit devices incorporating such transistors. Additionally, reducing the defects in the manufacture of the components of a typical transistor also lowers the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.
Generally, a set of processing steps is performed on a group of wafers, sometimes referred to as a xe2x80x9clot,xe2x80x9d using a variety of processing tools, including photolithography steppers, etch tools, deposition tools, polishing tools, rapid thermal processing tools, implantation tools, etc. The technologies underlying semiconductor processing tools have attracted increased attention over the last several years, resulting in substantial improvements.
One technique for improving the operation of a semiconductor processing line includes using a factory wide control system to automatically control the operation of the various processing tools. The manufacturing tools communicate with a manufacturing framework or a network of processing modules. Each manufacturing tool is generally connected to an equipment interface. The equipment interface is connected to a machine interface that facilitates communications between the manufacturing tool and the manufacturing framework. The machine interface can generally be part of an Advanced Process Control (APC) system. The APC system initiates a control script based upon a manufacturing model, which can be a software program that automatically retrieves the data needed to execute a manufacturing process. Often, semiconductor devices are staged through multiple manufacturing tools for multiple processes, generating data relating to the quality of the processed semiconductor devices.
During the fabrication process, various events may take place that affect the performance of the devices being fabricated. That is, variations in the fabrication process steps result in device performance variations. Factors, such as feature critical dimensions, doping levels, particle contamination, film optical properties, film thickness, film uniformity, etc., all may potentially affect the end performance of the device. Various tools in the processing line are controlled in accordance with performance models to reduce processing variation. Commonly controlled tools include photolithography steppers, polishing tools, etching tools, and deposition tools, etc. Pre-processing and/or post-processing metrology data is supplied to process controllers for the tools. Operating recipe parameters, such as processing time, are calculated by the process controllers based on the performance model and the metrology data to attempt to achieve post-processing results as close to a target value as possible. Reducing variation in this manner leads to increased throughput, reduced cost, higher device performance, etc., all of which equate to increased profitability.
Run-to-run control in semiconductor manufacturing is a type of batch control, where a batch may be as small as one wafer or as large as several lots of wafers. The standard output of a run-to-run controller is a process recipe. This recipe defines the set points for xe2x80x9clow-levelxe2x80x9d controllers built into the processing tool. In this way, the run-to-run controller supervises the tool controller by specifying required values for process variables such as temperature, pressure, flow, and process time. The tool controller initiates the activities necessary to maintain these variables at the requested values.
A run-to-run control setup may include a feedback loop where adjustments are made to the recipe parameters based on batch properties measured after processing. Generally, to control the processing of the wafer(s), it is desirable to know the xe2x80x9cprocessxe2x80x9d state (e.g., the processing tool state, wafer state, etc.) to process the next batch of wafers. The xe2x80x9cprocessxe2x80x9d state, however, is typically not measured directly but rather estimated based on the measurements from previously processed wafers. Because of time and cost issues, every wafer in the batch may not be measured. For example, in some implementations, the output characteristics of one out of every five processed wafers are measured. However, because the process state is estimated based on the measurements from previously processed wafers, the number of sample measurements considered can affect the accuracy of the estimation of the process state. The accuracy of the estimated process state in turn can affect how well the process can be controlled to achieve the desired target or goal. Thus, there is a need for a way of adjusting the number of sample measurements that are desired to control the process to achieve the desired objectives.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one embodiment of the present invention, a method is provided for adjusting a sampling rate based on a state estimation result. The method comprises receiving metrology data associated with processing of workpieces, estimating a next process state based on at least a portion of the metrology data and determining an error value associated with the estimated next process state. The method further comprises processing a plurality of workpieces based on the estimated next process state and adjusting a sampling protocol of the processed workpieces that are to be measured based on the determined error value.
In another embodiment of the present invention, an apparatus is provided for adjusting a sampling rate based on a state estimation result. An apparatus comprising an interface communicatively coupled to a control unit. The interface is adapted to receive metrology data associated with processing of workpieces. The control unit is adapted to estimate a next process state based on at least a portion of the metrology data, determine an error value associated with the estimated next process state and process a plurality of workpieces based on the estimated next process state. The control unit is further adapted to adjust a sampling protocol of the processed workpieces that are to be measured based on the determined error value.
In a further embodiment of the present invention, an article comprising one or more machine-readable storage media containing instructions is provided for adjusting a sampling rate based on a state estimation result. The one or more instructions, when executed, enable the processor to receive metrology data associated with processing of workpieces, estimate a next process state based on at least a portion of the metrology data and determine an error value associated with the estimated next process state. The one or more instructions, when executed, further enable the processor to process a plurality of workpieces based on the estimated next process state and adjust a number of the processed workpieces that are to be measured based on the determined error value.
In a further embodiment of the present invention, a system is provided for adjusting a sampling rate based on a state estimation result. The system comprises a controller and a processing tool. The controller is adapted to receive metrology data associated with processing of workpieces, estimate a next process state based on at least a portion of the metrology data and determine an error value associated with the estimated next process state. The processing tool processes a plurality of workpieces based on the estimated next process state. The controller is adapted to adjust a number of the processed workpieces that are to be measured based on the determined error value.